The most important decision when choosing a hot water heat pump: Refrigerant

Please don’t be scared off. I promise this is actually important (and kind of interesting). 

In fact, it’s one of the most important variables that affects the performance of a hot water heat pump (sometimes more than price).

This article is part of our series on hot water heat pumps. See all the other articles here.

Dummies guide to refrigerants

You might remember that hot water heat pumps work by soaking up heat from the air and then releasing that into the water tank. 

Absorb heat from outsideRelease heat into water tank

You can think of it like using a sponge to move water from one sink to another. 

Soak up heatRelease heat

What is refrigerant?

The refrigerant is a fluid inside the heat pump that does the actual absorbing and releasing. 

In other words, the refrigerant is the sponge. 


Heat pumps with different refrigerants are built differently, so refrigerant affects a bunch of things like performance, cost, and noise. 

In Australia, most hot water heat pumps use one of three refrigerants: R134A, Propane, and CO2. Let’s explain the differences and why you should care.


The most affordable hot water heat pumps use R134A. However, they don’t perform as well in lower temperatures. This is why many R134A have an electric booster element, to provide a little extra kick to get the water to 60°C when it’s really cold outside. 


Propane has a lower boiling point than R134A, which means it can extract heat more efficiently from colder air. Hot water heat pumps that use propane work better in colder temperatures but can also cost more.


CO2 has an even lower boiling point, and heat pumps that use CO2 have the best performance in colder temperatures. They are also the most expensive. This is partly because they need to be built in a way that lets them operate at the higher pressures required.

Global warming potential (GWP)

Because refrigerant is a gas at certain temperatures and pressures, releasing it into the atmosphere would contribute to climate change. 

So there’s something called GWP which measures how powerful a refrigerant is as a greenhouse gas compared to Carbon Dioxide (CO2).

A GWP of 1.0 means it’s a greenhouse gas that’s just as powerful as carbon dioxide. Naturally, CO2 refrigerants have a GWP of 1.

Propane is pretty good too, with a GWP of 3.

However, R134A has a GWP of 1,430, which means that for every kg released into the atmosphere, it’s equivalent to releasing 1.4 tonnes of carbon dioxide. Ouch. 

This doesn’t have much to do with the ordinary day-to-day use of the heat pump. Domestic hot water heat pumps are sealed units and tend to have low leak rates. 

The main problem is during end-of-life. Most units don’t need someone with a refrigerant handling licence to come and decommission the unit, they usually just end up going straight to landfills or metal recyclers where the refrigerant will be released into the atmosphere. 

For a heat pump that contains 750 grams of R134A refrigerant, that’s equivalent to releasing over a tonne of CO2 into the atmosphere. That’s a flight from Melbourne to Auckland. 

High GWP refrigerants like R134A are gradually being phased out in Australia and globally. 

While a limited amount can still be imported into Australia, it shows where the industry is heading. Over time, it will be increasingly difficult to get parts and repairs for heat pumps using R134A as a refrigerant.

Refrigerant vs price

Because R134A is lower performing and CO2 is higher performing, this naturally creates a couple of price points as the more expensive brands tend to use CO2, while the more affordable brands will tend to use R134A or Propane. 

RefrigerantR134AR290 (Propane)R744 (CO2)
Cost$33 – $3000 after rebates$1000 – $3000 after rebates$4000 – $8000 after rebates
Noise~50 dB (like a dishwasher)43 dB – 50 dB~37 dB (whisper quiet)
Minimum effective operating temperature5°C-7°C-15°C
Global warming potential (GWP)1,43031

Generally speaking, any hot water heat pump is better than no hot water heat pump. 

However, we like heat pumps with Propane or CO2 refrigerants as they are more environmentally friendly, often quieter, and perform better at low temperatures. 

Next steps

Now that you understand the importance of choosing the right refrigerant, read about which brands are good.

Or if you want to know whether a hot water heat pump is worth it for your house, get an instant cost, savings and rebates estimate.